The present invention pertains to mechanisms in firearms that control or limit the movement of the firearm “bolt” element. In many typical firearm designs, a magazine is used to store and feed ammunition into a firing chamber. In many manual as well as semi and fully automatic firearms, a bolt moves backward and forward between each shot, propelled by recoil or expanding gas or a recoil spring. When the bolt moves forward, it moves a cartridge from the magazine and pushes it into the chamber. During firing, the bolt blocks and seals the chamber. When the bolt moves back, the spent ammunition casing is removed from the chamber and ejected from the firearm. Typically, after the last round in the magazine is fired, a floor plate of the magazine is pushed upward by spring action to contact and lift a bolt “stop” or “catch” that is mounted within the firearm receiver. In this lifted position, the bolt stop holds the bolt rearward of the magazine to allow viewing of the chamber and for other purposes. After an empty magazine is removed and a full magazine inserted into the firearm, the bolt must be allowed to move forward to chamber a new round of ammunition.
Various rifles known by the designations “M16” or “M4” or “AR15” include a bolt stop that operates in the above manner. These rifles include a bolt stop that is pivotably secured within the rifle receiver and is rotated upward to block forward travel of the rifle bolt as discussed above. After a new full magazine is inserted, the bolt stop is manually rotated downward to allow the bolt to move forward under spring biasing to chamber a round from the magazine. On these firearms, the bolt stop release is located on the left side of the rifle receiver, intended to be operated by the left hand. This configuration is limiting and is often difficult to use with a single hand while aiming the firearm. As well, this configuration is problematic for left-hand use of the firearm. Rifles having similar platforms and sharing the above described bolt stop and release mechanism are for convenience here referred to as M16/M4 rifles.
What is desired is a similar firearm with a bolt stop release that is operable from both sides. Because there are a substantial number of existing firearms using the prior “left side only” release mechanism, it would be valuable to enable simple modification of these firearms to provide ambidextrous stop release operation.